November 29, 2021

First snowfall in the plains this weekend

Through Regis CREPET, meteorologist

Winter will mark a first offensive this weekend on France. It will be a fairly marked cold for the season but above all very humid from the north-west. This configuration is suitable for snowfall in the plains, and abundant snowfall on all our mountains at low altitude. Here’s what to know, especially if you’re planning to drive this weekend.

Snow is not rare at the end of November in the plains, where some years have sometimes seen thicknesses of several tens of centimeters, causing circulation difficulties. In this regard, the end of November 2010 was historic along the Channel coast, and in particular in Normandy, where 50 cm of snow had been recorded in Cherbourg (50) for example. In November 1999, hundreds of heavy goods vehicles were stranded on the A7 motorway in the Rhône valley. This time, we will be very far from these remarkable scenarios, with a fairly classic situation at this time of the year, but which you will have to be wary of if you have to travel on the first reliefs in the east and center-east. of our country. Indeed, this episode is the first of the season, and it can surprise. At the same time last year, a first snowfall occurred on November 28, but it only concerned the Grand Est.

A succession of snow showers over France

The winter situation that we will experience this weekend is linked to the passage of several disturbances descending from the British Isles to the south of France. In a very windy flow with a mass of cold air, these disturbances will bring many rainy passages in the plain, mixed with melting snow. From the first reliefs, generally between 200 and 300 meters above sea level, some snow showers may whiten the soils, which are called “showers”. Near our massifs, from an altitude of 500 to 600 m, it will be repetitive snowfall bringing a layer of several centimeters that will have difficulty melting. Then, above an altitude of 800 m, the viability will be winter, which can lead to traffic difficulties in mid-mountain areas because snow will fall regularly with wind: crossing mountain passes will therefore be made difficult. .

Snow from Saturday morning

The first disturbance will quickly cross France from the Channel coasts to the Pyrenees and the Alps between Friday evening and Saturday morning. We therefore await the appearance of the first snowflakes at the end of the night from Friday to Saturday, and Saturday morning, in the Ardennes, the Grand Est plateaus, the Northern Alps and the Monts d’Auvergne, as well as in the Pyrenees. The snow will therefore replace the rain in places with the cooling of the air mass. We could thus raise from 2 to 5 cm Saturday morning between the Ardennes and the plateaus of the Grand Est.

A regime of showers for Sunday

After the passage of the cold front on Saturday morning, the day will unfold under showers and sleet, sometimes mixed with sleet and flakes to the plains. But, with positive daytime temperatures, this snow will only hold up in areas above 400 m altitude. The risk of having snow below this altitude will occur at night and in the morning, at the coldest hours of the day. This may be the case on Saturday evening in the hills going from inland Brittany to the Picardy plateaus and the reliefs of Artois.

For Sunday In the morning, we could find these snow showers between Limousin, Rhône-Alpes-Auvergne and all the Grand Est. With the cooling at the start of the day, the flakes could reach the plain and fall on Limoges, Clermont-Ferrand or even the Val de Saône and Lyon, without holding on to the ground. But from the first heights, the snow will be able to hold and bring from 2 to 7 cm towards 500 m of altitude. The city of Saint-Etienne, in the Loire, could be whitewashed by a few centimeters on Sunday morning. For the heart of the alpine valleys, like Grenoble and Chambéry, the snow should hold only on the very first heights, but a priori not in the center of the agglomerations. Nevertheless, by isothermal phenomenon, there is a risk that the snow will hold up to these central-eastern cities on Sunday morning, In these central-eastern regions, the snowfall could last a good part of the day on Sunday, which could bring significant accumulations from the first reliefs (10 cm possible at an altitude of 800 m).

In summary, it should be remembered that this first winter offensive of the season does not present an abnormal character this time of the year, but will require particular caution if you have to travel in the east of France and near the reliefs. But for mountain resorts and snow enthusiasts, this weekend will be a real godsend.

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